1. Field of the Invention
The present invention relates to a chemical mechanical polishing (CMP) method and, more particularly, to a method that uses a first-CMP step to form an edge-thicker and center-thinner profile on a wafer and then uses a second-CMP step to compensate for the non-uniformity on the wafer.
2. Description of the Related Art
As IC devices become smaller with highly integrated interconnections, uniformity control in planarization technique becomes much crucial because there are more limitations in subsequent process window, such as depth of focus (DOF) during lithography. Chemical mechanical polishing (CMP), combining chemical reaction and mechanical polishing to planarize the uneven surface of a layer of dielectric or metal on a wafer, benefits controls in subsequent processes, such as deposition, highly-precise exposure and etching stop. FIG. 1 is a schematic diagram showing a polishing apparatus of CMP system according to the prior art. A polishing apparatus 10 comprises a platen 12, a polishing pad 14 attached to the platen 12, and a polishing carrier 16 installed over the platen 12. During CMP, a wafer 18 is placed on the platen 12 and pressed on the polishing pad 14 by the polishing carrier 16. The polishing carrier 16 rotates in a rotating direction A and provides a pressure P to drive the wafer 18. Furthermore, the platen 12 is rotated in a rotating direction B that is the same as the rotating direction A. In addition, slurry 20 is constantly supplied to the platen 12 by a delivery system 22. Therefore, on the platen 12, combining the chemical reaction provided by the slurry 20 and the chemical polishing on the wafer 18, the raised portions on the wafer 18 are removed to achieve planarization.
The uniformity control during CMP depends on the height and density of the raised portions on the predetermined polishing surface, the variation of critical dimension (CD), and the edge-thicker and center-thinner profile of the predetermined polishing surface caused by the useless pattern formed on the edge of the wafer. In order to improve the uniformity control in CMP, the traditional method tunes process parameters, such as pressure forced by the polishing carrier 16, the rotating speed of the polishing carrier 16 and the platen 12, the flowing speed of the slurry 20, the chemical composition of grinding particles in the slurry 20, process temperature and the material of the polishing pad 14. However, the relation between these process parameters is complicated and varied with surrounding circumstances, hence it is difficult to obtain a definite relation because experimental difficulties are encountered and costly measuring facilities are needed. Although various forms used for the polishing carrier and the control of multiple-polishing zones are well developed to improve the uniformity in CMP, they still cannot achieve the expected planarization.
Thus, a CMP process parameter unrelated to the above-mentioned CMP parameters and able to be tuned in various polishing apparatus solving the aforementioned problems is called for.
The present invention provides a method that uses a first-CMP step to form an edge-thicker and center-thinner profile on a wafer and then uses a second-CMP step to compensate for the non-uniformity on the wafer.
In the method of improving uniformity control in CMP, a CMP apparatus is provided with at least a platen, a polishing pad disposed on the platen and at least a polishing carrier installed over the platen. The platen rotates in a first rotating direction, and the polishing carrier is used to press a wafer on the polishing pad and drive the wafer to rotate. The present invention employs a first-CMP step and a second-CMP step to achieve planarization. The first-CMP step is used to finely modulate the thickness distribution of the depositing layer to decrease the difference in thickness between the edge region and the center region on the wafer. The second-CMP step is used to carry out the main polishing process on the depositing layer to obtain the required planarization and height.
Accordingly, it is a principal object of the invention to provide a CMP process with a first-CMP step and a second-CMP step to compensate for the non-uniformity on the wafer.
It is another object of the invention to provide a CMP method to obtain a required planarization and height on the wafer.
Yet another object of the invention is to provide a CMP method to improve uniformity control on the wafer.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.